According to Du Cange, the designation captal (capital, captau, capitau) was applied loosely to the more illustrious nobles of Aquitaine, counts, viscounts, &c., probably as capitales domini, "principal lords", though he quotes more fanciful explanations.
As an actual title, the word was used only by the seigneurs of Trene, Puychagut, Epernon and Buch.
[1] Buch was a strategically located town and port on the Atlantic, in the bay of Arcachon.
In 1364, he ravaged the country between Paris and Rouen, but was beaten by Bertrand du Guesclin at the Battle of Cocherel (1364) and taken prisoner.
In 1367, he took part in the Battle of Navarrete (1367) in which Du Guesclin was taken prisoner, the captal being entrusted with his safe-keeping.